Need Brake Bleeding Education

[schu]

Glad you fixed it Rob. I have a grove parking brake on mine, but now that I know about your issue, I'll make sure I can blow freely through the line while open before I put brake fluid in it.

schu

[quadra]

I don't know how I missed that last image Rob, but glad you found the problem!

[Nev]

Glad you resolved this Rob. I’ll be keeping the parking brake on mine, but I do think the valve arm needs to be adjusted to be in the correct position, with the cable then locked in position so it can’t move.

We’re all standing by a first flight video All the best with it !

[zkelley2]

PROBLEM SOLVED.

I eliminated the Matco Parking Brake and I can now watch the calipers compress and decompress as I work the toe brakes.

Good Lord!!!

I cannot say that I endorse the Matco PB. Pretty scary to think about pressure in the brake lines on short final. I'll be buying a nice set of wheel chocks...

Tailwheels flip all the time because of faulty or wrongly set parking breaks. I'm not a fan personally.

[Bcone1381]

Good to know it common to go without. I removed my PB valve in order to simplify and because I did not like my install....I was wondering if I was an outlier not having one.

[Utah-Jay]

Go fly that thing!

[Nev]

Tailwheels flip all the time because of faulty or wrongly set parking breaks.

You certainly got me thinking. I googled and found a couple of accidents due to landing with the Park Brake set. One after the pilot had locked the wheels to skim across a lake....... Another when the valve arm wedged against a brake line.

Definitely the manoeuvre has a greater downside on a taildragger, but the accident reports I found seemed to be isolated occurrences. Perhaps some are going unreported.

Removing the Park Brake could be removing one risk, and replacing it with another.

On my installation, the Park Brake valve is under the floor. So if something went mechanically wrong in the air, (and I was able to detect it) I wouldn’t necessarily be able to do anything about it. I’m thinking a cable going over center, or the cable sheath moving through an Adel clamp etc. Those that have valves mounted on the firewall could easily reach and sort out this condition.

Has anyone ever needed to physically access their Park Brake valve in anger valve while airborne ?

One idea is to install a pressure transducer in the hydraulic lines, downstream of the valve. This would indicate anytime the brakes are actually on, and would be an indication in the air if the Park Brake is somehow set. Is this overkill ? How would I go about installing such a transducer? Any other ideas?

[Mark Goldberg]

I do know of one ground loop in a BH that was attributed to a parking brake issue. Mark

[Nev]

Mark, do you know what the issue was with the parking brake ? Was it inadvertently let ON ? Or a mechanical issue with it ?

[noema]

I definitely want to install a parking brake. There are too many occasions where I fly that involved parking the plane at an incline. So just getting some choke in first requires some parking brake.

That being said, not only can you flip the plane on landing. These guys managed to wreck it on takeoff because the brake was halfway on. https://youtu.be/mMG2HwIFfgU

The more I think about this the more I like the Husky parking brake. You get your fingers full of grease and occasionally scratch them up on a sharp edge but seem otherwise fool-proof. It has two latches on the pax master cylinders that hold the cylinders in a compressed position. They are designed in a way to release as soon as you hit the brakes.

[robcaldwell]

Removing the Park Brake could be removing one risk, and replacing it with another.

I'll take that risk. This experience has scared the shit out of me! Pumping the brakes on final, unwittingly ensuring that you have just locked the parking brake valve? No thanks.

My lesson and take away from this experience is this, I will NEVER install anything that goes in the middle and interrupts the brake fluid system. However, if I can incorporate an external pressure force that manipulates the brake system, possibly I will consider that. I understand the old Cessna 140's had something similar to that.

[Sir Newton]

Piper park brake adds an extra master cylinder into the system that has mechanical locking system similar to your flaps handles.

[gregc]

I cursory review of the NTSB database seems to indicate that the mechanical approach with tabs or latches is no better than the hydraulic lock approach.

[alaskabearhawk]

FWIW, I have Parker valve installed and will leave it in. There have been so many times I have parked on a slope near fuel pumps wishing I had one. That alone is worth it to me. Read under “Full Description” https://ph.parker.com/us/en/park-brake-valves

[zkelley2]

Are you guys parking on 30 degree inclines or something? Turn the plane sideways to the hill. No parking break needed.

[JimParker256]

Turning sideways to the hill is not always an option. I went to a fly-in in a Commander 114, and when I got there, there was only one tie-down spot available. It was on about a 10º slope, between two other airplane, and pointing at another row of airplanes in front. With no parking brake, and no one around to assist me, I wound up having to carefully choreograph my exit from the airplane (with wheel chocks in hand) so that a hit the ground rolling under the wing to drop the wheel chock in front of one gear, then quickly roll to the other side and get it under the other gear. I managed to acquire a few bruises along the way, and of course there was a small oily puddle I rolled through... It would have been a little easier with a Bearhawk, but still...

I think if the Beringer parking brake valve is properly installed, it is pretty reliable. I cannot imagine any scenario other than pilot error that would allow the parking brake to be set inadvertently. That valve is not a "one-way" valve, it is functionally like a pair of fuel shutoff valves in parallel. To engage the parking brake, you have to pressurize the brake lines by holding the brakes, then turn the parking brake arm to shut those valves. The result is that the pressure you just created becomes trapped in the brake lines, keeping the brakes engaged.

Applying the brakes with the parking brake already engaged does nothing - fluid cannot flow through, so the brakes are not activated. Likewise, applying the parking brake without first building pressure in the brake lines (pressing the brakes) merely locks in the "atmospheric" pressure to the brake lines – which should NOT result in any braking action.

Of course, pilot error is still a possibility, but it would take a significant screw-up (IMHO) to inadvertently engage the parking brake by pressing the brakes, then pulling the parking brake lever, all without the pilot noticing...

[Battson]

PROBLEM SOLVED.

I eliminated the Matco Parking Brake and I can now watch the calipers compress and decompress as I work the toe brakes.

Good Lord!!!

I cannot say that I endorse the Matco PB. Pretty scary to think about pressure in the brake lines on short final. I'll be buying a nice set of wheel chocks...

The Grove parking brake gets my full recommendation. I have never had a problem with any Grove gear.

[Battson]

Are you guys parking on 30 degree inclines or something? Turn the plane sideways to the hill. No parking break needed.

In fact, you only need a few degrees slope or a strong wind to require a brake. Without brakes it would be a nightmare, chocks - no way.... Honestly.

Anyone parking near me without a brake gets because it's my plane, not theirs, which is at risk.

[zkelley2]

In fact, you only need a few degrees slope or a strong wind to require a brake. Without brakes it would be a nightmare, chocks - no way.... Honestly.

Anyone parking near me without a brake gets because it's my plane, not theirs, which is at risk.

Something like 3000 hours SEL. I've never used a parking brake. There's always an option. Littererally never have been in a position to need one. No plane I own will ever have one because of the exact issue in this thread. It's not remotely rare.

They're great on the jet but that's a wildly different environment, but it's not because of slopes.

[gregc]

I think this is an interesting topic not so much for the specifics but rather as a approach to making a build decision.

1) Does something add weight and/or complexity? Complexity has to include operational issues as well. Chocks are clearly mechanically simpler but using them on a slope in the wind may not be simple.

2) Do I understand how the particular solution/system works? In this case there are engineering diagrams that support JimParkers explanation of how hydraulic parking brake locks function. Rob’s problem can be explained if the parking brake lever was in the transition zone and fluid flow was restricted enough to cause a slow pad release. The heat generated during taxi soon overcame the entire system.

3) Is there data available on failure and/or risk? How common is the solution or system? Nev didn’t find much on-line and there is little data in the NTSB database to indicate a significant problem. Parking brakes are very common. Still we have to be careful here - there may not be enough data to give an accurate picture.

4) My behavior. Would I be as diligent as zkelley and use an alternative every time or might I personally be better overall with an easier option (even a perfect system is no good if you don’t use it) .

5) Finally, how do I prioritize risk. Like Battson, I am generally more worried about damaging someone else’s person or property than my own so I have to factor this in.

For me, this adds up to having a parking brake but for you it may not.

[BravoGolf]

On one twin that I flew there was a brake hydraulic pressure gauge. One step of the before landing check was step of the brakes and verify a pressure increase AND decrease. A fluid pressure transducer / gauge could be added to the brake hydraulic system of our aircraft.